@@ -504,6 +504,26 @@ static int __init smp_cpu_setup(int cpu)
static bool bootcpu_valid __initdata;
static unsigned int cpu_count = 1;
+int arch_register_cpu(int cpu)
+{
+ struct cpu *c = &per_cpu(cpu_devices, cpu);
+ acpi_handle acpi_handle = ACPI_HANDLE(&c->dev);
+ int ret;
+
+ if (!acpi_disabled && !acpi_handle)
+ return -EPROBE_DEFER;
+ if (acpi_handle) {
+ ret = acpi_sta_enabled(acpi_handle);
+ if (ret) {
+ /* Not enabled */
+ return ret;
+ }
+ }
+ c->hotpluggable = arch_cpu_is_hotpluggable(cpu);
+
+ return register_cpu(c, cpu);
+}
+
#ifdef CONFIG_ACPI
static struct acpi_madt_generic_interrupt cpu_madt_gicc[NR_CPUS];
On ARM64 virtual CPU Hotplug relies on the status value that can be queried via the AML method _STA for the CPU object. There are two conditions in which the CPU can be registered. 1) ACPI disabled. 2) ACPI enabled and the acpi_handle is available. _STA evaluates to the CPU is both enabled and present. (Note that in absences of the _STA method they are always in this state). If neither of these conditions is met the CPU is not 'yet' ready to be used and -EPROBE_DEFER is returned. Success occurs in the early attempt to register the CPUs if we are booting with DT (no concept yet of vCPU HP) if not it succeeds for already enabled CPUs when the ACPI Processor driver attaches to them. Finally it may succeed via the CPU Hotplug code indicating that the CPU is now enabled. Suggested-by: Rafael J. Wysocki <rafael@kernel.org> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> --- v5: New patch. --- arch/arm64/kernel/smp.c | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+)